Hydroentangling or spunlacing is a technique introduced during the 1970'ies, see e.g. CA patent no. 841 938. The method involves forming a fibre web, which is either drylaid or wetlaid, after which the fibres are entangled by means of very fine water jets under high pressure. Several rows of water jets are directed against the fibre web, which is supported by a movable wire or perforated drum. The entangled fibre web is then dried. The fibres that are used in the material can be natural fibres, especially cellulosic pulp fibres, manmade staple fibres, which may be synthetic, e.g. polyester, polyamide, polyethylene, polypropylene, or regenerated staple fibres, e.g. viscose, rayon, lyocell or the like, and mixtures of pulp fibres and staple fibres. Hydroentangled materials can be produced in high quality to a reasonable cost and depending on the type of fibers used they possess desired properties like high liquid absorption, liquid distribution, liquid inlet, softness etc. They can e.g. be used as wiping material for household or industrial use, as disposable materials in medical care, and in hygiene articles as topsheet materials and absorbent components etc.
Topsheet materials in absorbent articles like sanitary napkins, diapers, pant diapers, incontinence guards etc. are designed to distribute and move body fluids rapidly through them and into an underlying absorbent structure for storage. The more rapid, directionally controlled and thorough this transport is, the drier and cleaner the surface of the article and the greater is the comfort experienced by the wearer. Nonwoven fabrics used as topsheet often need to be modified, for example apertured, corrugated and/or treated with fluid modifying agents, such as surfactants or softeners in order to maximize its fluid handling and comfort properties. The softness of nonwoven fabrics can be increased by mechanical and/or chemical treatment.
The skin is sensitive to the changes in force required to deflect the fibres that are in contact with the skin surface. The bending stiffness of a fibre is a function of its fineness. Accordingly, for a given polymer, a decrease in filament linear fineness tends to increase its perception of softness. Spunbond and meltblown technologies are available that produce fine filaments having a fineness of 1 dtex or less. There are also known other techniques for producing nonwoven materials comprising microfibers.
U.S. Pat. No. 6,270,623 discloses an method of making an apertured nonwoven fabric useful as a topsheet on an absorbent article, wherein a wet sheet is formed from a wet slurry containing a mixture of pulp fibres and synthetic microfibers having a length between 7 and 30 mm and a fineness of 0.1-0.8 denier. The sheet is subjected to hydroentanglement. The web is apertured either as a result of hydroentanglement or by piercing with needles.
US 2003/0125687 discloses a multiple zone apertured web used as topsheet on an absorbent article. The web has at least two distinct zones of different hole sizes. The apertures may be formed by placing the web on a patterned support member and then subject it to high fluid pressure, which means hydroentanglement.
EP-A-0 418 493 discloses a nonwoven composite fabric comprising one layer selected from a web of textile fibres and a net of polymeric filaments and at least one web of meltblown microfibers, combined by hydroentangling. The web may be apertured by hydroentangling and holes of different sizes may be produced. The fabric may be used as a topsheet on an absorbent article.
US 2005/0148969 describes a combined cover layer and absorbent layer for an absorbent pantiliner comprising a mixture of hydrophilic and hydrophobic microfibers, wherein a larger quantity of hydrophobic microfibers than hydrophilic microfibers are located at the top surface of the cover layer.
However there still exists a need for improvement of nonwoven fabrics, especially adapted as topsheet materials on absorbent articles, with respect to softness, liquid inlet and rewet properties.